An increase in the efficiency of a thermal power machine, e.g. a gas turbine, is directly dependent on an increase in the working temperature of the thermally loaded components and therefore, in the case of a gas turbine, on the combustion gas temperature of the combustion chamber and the turbine which follows it. Despite improvements in materials which are able to withstand high temperatures, cooling technology also needs to be improved in order to keep the materials temperature within a safe range when thermally loaded components of this type are in operation. Cooling passages are used for this purpose and have to be fed with cooling fluid, for example from the compressor. It is attempted in this context to achieve the maximum possible cooling effect combined with the minimum possible losses in power of the overall system. For this purpose, specific improved heat-transfer techniques, such as for example fins in the cooling passages, are used.
GB 2 165 315 has disclosed blades or vanes in which cooling fluid is passed from the trailing-edge region of the blade or vane to the leading-edge region via cooling passages formed by partition walls and is then blown out via openings in the head of the blade or vane. To sufficiently cool the trailing-edge region of the blade or vane, air is blown out of the trailing edge of the blade or vane. Diverter blades are provided in order to divert the cooling fluid into the cooling passages.
In general terms, cooling passages which in many instances run substantially parallel and which are connected via diverter passages are used in thermally loaded components, e.g. blades or vanes of turbines. These diverter passages are configured in such a way that the pressure loss involved in the diversion is minimal and the heat transfer is as homogeneous as possible, in order to avoid local hot zones. To achieve this, in many cases diverter blades are arranged in the region of the diverter passages. However, these diverter blades are very fragile and are difficult to produce by casting, even in the case of large components, such as for example large blades or vanes of stationary gas turbines. By way of example, during cooling of the casting following the casting operation, stresses may form in the casting, since the inner parts, which are of relatively small dimensions, and the outer parts have different cooling rates. In some cases, these stresses may cause cracks to occur in the inner structures, with the result that the casting cannot be used. If the defects are not noticed, the casting may break in use and may then, for example in the case of blades or vanes, cause damage to further blades or vanes and the turbine.
Cooling of turbine blades is known for example from U.S. Pat. No. 3,171,631 or from U.S. Pat. No. 5,232,343.